Chemotaxis, a process in which cells migrate toward higher concentrations of chemoattractants, is important for a variety of physiological events such as axon guidance, wound healing, and tissue morphogenesis. Inappropriate chemotaxis leads to many human diseases including tumor metastasis, asthma, arthritis and atherosclerosis. The long-term goal of our research is to reveal the molecular mechanism of chemotaxis and to understand the pathogenesis of chemotaxis- related human diseases. Using Dictyostelium discoideum as our experimental model system, we have demonstrated that phosphatidylinositol 3,4,5 triphosphate (PIP3) plays a critical role for intracellular signaling in chemotaxis. PIP3 is highly enriched at the leading edge of cells and activates downstream signaling events such as remodeling of the actin cytoskeleton. We have demonstrated that the intracellular level and localization of PIP3 are regulated by a lipid phosphatase, PTEN. PTEN is located at the rear end of chemotaxing cells and restricts the production of PIP3 at the leading edge. The local accumulation of PIP3 stimulates actin polymerization to extend pseudopods toward the source of chemoattractant. To date, it is unknown how the localization and activity of PTEN are regulated, and how PIP3 signaling is translated into reorganization of the actin cytoskeleton. In this research proposal, we will use a combination of genetics, biochemistry, cell biology and proteomics to achieve the following specific aims: 1) To determine how phosphorylation regulates the localization and activity of PTEN; 2) To define the functions of two proteins required for chemotaxis - Huntingtin and GxcT, a novel guanine nucleotide exchange factor for Rho GTPases; 3) To identify novel components that link PIP3 signaling and the actin cytoskeleton using proteomic approaches as well as genome-wide characterization of PH-domain containing proteins. The outcomes of our research are expected to provide novel insights into molecular mechanisms of chemotaxis and may lead to development of chemotaxis-based treatments for cancer and inflammation. PUBLIC HEALTH RELEVANCE: We study chemotaxis, a process in which cells sense extracellular chemical compounds and move toward the source of chemicals. Chemotaxis is highly relevant to development and maintenance of healthy human body as well as the pathogenesis of many diseases such as cancer, asthma, arthritis and atherosclerosis. The long-term goal of our study is to understand how chemotaxis works and how defects in chemotaxis cause human diseases using a variety of approaches including genetics, biochemistry, cell biology and proteomics.